We have previously shown that the conversion of glucose to fat is an energy-yielding process which can be limited by ADP availability. Thus, increased ADP conversion to ATP through fatty acid oxidation when FFA levels are high could inhibit lipogenesis by diminishing ADP availability, thereby explaining the inhibitory effect of FFA on this process. The aim of our studies is to elucidate the physiological role of FFA in the regulation of adipose tissue lipogenesis. Since circulating FFA are largely bound to albumin, a method for the measurement of unbound FFA is being developed so that the metabolic effects of FFA may be related to their effective availability to tissues. According to recent studies, lipogenesis in human adipose tissue is very limited, in marked contrast to rat adipose tissue. However, the combined effects of age and diet in reducing lipogenesis in the rat need to be adequately appreciated, and will therefore be investigated. If adipose tissue lipogenesis in full grown rats maintained on a human-type diet (40% of calories from fat) is reduced to rates comparable to those measured in man, the rat would regain much greater significance as a model system for the study of adipose tissue metabolism and its role in total body metabolism and obesity.